Peristaltic pumps are used in numerous applications that require low shear pumping, portability, ability to run dry, ease of cleaning, accurate dosing, etc. These applications can be found in industries ranging from pharmaceutical manufacturing to food processing to water treatment.
The basic principle of peristaltic pumping involves the rotation of a central rotor containing either rollers or fixed shoes against a resilient elastomeric tube surrounding the rotor that is compliant enough to allow for complete collapse from the rotating rollers, and yet elastic enough to recover to a circular cross-section (referred to as restitution) once the rollers pass, thus enabling the next segment of tubing to fill with the process fluid and maintain flow.
Although peristaltic pumps have many advantages, they do suffer from some drawbacks. In particular, if tubing is not properly installed in the pumphead, the tubing can be damaged by the rotor and cause premature failure. This is particularly true when the tubing is twisted upon installation or the tubing elongates during operation within a fixed cavity pumphead.
Another disadvantage of peristaltic pumping is the relatively short flex life of the tubing materials. The flex life often dictates how frequently the tubing needs to be replaced and thus affects the maintenance costs. Many devices have been developed to extend the life of pump tubing. In particular, manufacturers have used spring loaded rollers and spring loaded tracks to reduce the load on the tubing. However, in all prior art, the tubing is held rigidly in the pump housing. The rigid anchoring of the tubing requires the tubing to stretch significantly upon compression and restitution in the pumphead.
Green (U.S. Pat. No. 6,494,692 B1) discloses a peristaltic pump with tubing elements that are easily installed and removed. The elements are equipped with non-circular plastic flanges that are positioned in complimentary recesses in the pump head to prevent lengthwise movement of each end of the tube relative to the pumphead housing and inhibit twisting of the tube. This invention, however, overlooks the fact that many tubing materials grow in length upon flexure, and become entangled in the pumphead, thus leading to premature failure. It also requires very tight tolerances on the element length to avoid diminishing the intended flex life.
Calhoun (U.S. Pat. No. 5,388,972) also discloses a peristaltic pump with elements to precisely control the length of tubing operated upon by the pump. Recesses are provided on either side of a tube element having different sizes and/or shape to control the orientation of the tubing.
Fulmer (U.S. Pat. No. 5,356,267) discloses a removable cartridge that includes a length of tubing and a collapsing device such as a rotor. He discloses the use of flanges that grip the tubing to communicate with slots in the housing, thus securing the tubing in place. This invention allows for rapid replacement of tubing elements as well.
Fittings for tubing are well known in the industry. Cooke (U.S. Pat. No. 4,498,691) describes hydraulically crimped fittings that can be used to securely hold peristaltic pump tubing for the instant invention. Flanges can also be injection molded around pump tubing elements at convenient locations along the tubing axis to secure the tubing in the inventive pumphead. Other means of locating the tubing in the peristaltic pump head can be used as well.
A pump in accordance with the present invention will enable engagement of fitted tubing elements with a peristaltic pumphead. The inventive pump will accommodate the viscoelastic properties of tubing materials that either resist elongation or result in excessive elongation upon pumping.